In addition to providing an acceptable rate of reaction at relatively low pressures and temperatures, a hydrocarbonylation catalyst should provide good catalytic activity over a sufficiently long period of operation of the process to make its use economically feasible. Further, in the case of hydroacylation processes, the catalyst should also provide the degree of ketone selectivity required for a particular application. Acceptable levels of ketone selectivity are widely variable and can range from ketone yields as low as 5 weight percent of the aldehyde and ketone produced up to ketone yields of 40 weight percent or more of aldehyde and ketone produced.
British Patent No. 1,181,806 discloses a process for the production of alcohols and/or aldehydes by the reaction of an alpha olefin, carbon monoxide and hydrogen in the presence of a square planar complex of monovalent rhodium containing at least one carboxylate ligand derived from aliphatic, substituted aliphatic, aromatic or substituted aromatic carboxylic acids, with the carboxylic acids of choice being acetic, propionic, pivalic and isobutyric acids. British Patent '806 further discloses that the square planar rhodium complex may further comprise at least one trialkyl phosphine, triaryl phosphine, trialkyl arsine, triaryl arsine, trialkyl stilbine, triaryl stilbine, pyridine or amine. Preferred catalysts of this British Patent are compounds of the formula: EQU Rh(R R'R"P).sub.2 (CO)R'"COO
wherein R, R', R", and R'" are alkyl or aryl groups any number of which may be identical. Disclosed reaction conditions include temperatures of between 60.degree. C. and 200.degree. C. and pressures between 300 psig and 1,000 psig. The patent exemplifies as suitable catalysts rhodium bis (tri-n-alkyl phosphine) carbonyl carboxylates and rhodium bis-(tri-n-alkyl amine) carbonyl carboxylates, all of which have a carboxylic acid to rhodium mole ratio of 1.
The square planar compounds of this British Patent are further characterized as having a characteristic peak at 1970 cm.sup.-1 in their infra red spectra. For comparative purposes, infra red spectra of trans- Rh (O.sub.2 CC.sub.6 H.sub.4 p-NO.sub.2)(CO) ((C.sub.6 H.sub.5).sub.3 P).sub.2, a square planar compound having a characteristic peak at 1970 cm.sup.-1 (Spectrum B), and an isolatable complex intermediate of the present invention, having a mole ratio of carboxylic acid to rhodium of at least about 2, (Spectrum A) are provided herein in FIG. 1. As shown by FIG. 1, Spectrum A lacks the peak at 1970 cm.sup.-1 which is characteristic of the square planar rhodium compounds of British Patent '806. In use, the catalysts exemplified by British Patent '806 tend to become deactivated after relatively short periods of operation.
U.S. Pat. No. 4,224,255 to Smith discloses a rhodium catalyzed process for hydroformylating alpha olefins by reaction with hydrogen and carbon monoxide wherein aldehyde formation is enhanced by the addition of an acidic compound to the reaction medium to suppress olefin hydrogenation. The acid of choice in the Smith patent is o-phthalic acid. Disclosed process conditions include pressures of one atmosphere up to 10,000 psig and temperatures of 10.degree. C. to 250.degree. C., with preferred conditions being pressures of from about 300 psig to about 1200 psig and temperatures of from about 70.degree. C. to about 250.degree. C. The processes exemplified by the Smith patent generally sustain commercially unacceptable levels of rhodium deactivation after relatively short periods of operation.
British Pat. No. 1,181,806 and U.S. Pat. No. 4,224,255 notwithstanding, the presence of acids in a hydroformylation reaction medium has been disclosed as having a deleterious effect on catalyst activity. U.S. Pat. No. 3,555,098 to Oliver et al. describes a hydroformylation process employing as a catalyst, a complex of a biphyllic ligand (e.g., a triaryl phosphine) and rhodium wherein the reaction medium is treated with an aqueous alkaline wash to extract carboxylic acid by products from same. Oliver et al. disclose that unless removed, accumulated carboxylic acid by product will deactivate the catalyst, see U.S. Pat. No. 3,555,098 at column 1, lines 13 to 25; and column 1, line 64 to column 2, line 18. The deactivation of rhodium catalysts by acid by-products is also disclosed in "Rhodium Catalyzed Low Pressure Hydroformylation of Vinyl Esters: Solvent and Phosphine Effects on Catalyst Activity, Selectivity and Stability", by A. G. Abatjoglou et al., Journal of Molecular Catalysis, Vol. 18 (1983) at pp. 383 to 385.
Much of the art relating to rhodium-catalyzed hydroacylation processes suggests that the use of relatively high pressures and/or temperatures is critical to obtaining desirable ketone selectivity and/or acceptable reaction rates. For example, German Pat. No. 1,793,320 disclosing the rhodium-catalyzed reaction of ethylene, carbon monoxide and hydrogen to produce ketones, requires the use of pressures of from about 200 atmospheres to about 300 atmospheres and temperatures of from about 150.degree. C. to about 200.degree. C.
Although hydroacylation processes which utilize more moderate conditions of temperature and/or pressure are known in the art, such processes generally do not employ a rhodium catalyst. For example, U.S. Pat. No. 2,699,453, to Naragon et al. discloses a process for producing diethyl ketone by reacting ethylene, carbon monoxide and hydrogen in the gas phase at a mole ratio of ethylene to carbon monoxide of at least 1.5 and a mole ratio of ethylene to hydrogen of at least 0.67. The process is disclosed as being carried out at a temperature below 300.degree. F. and at a pressure that can be relatively low (i.e., as low as about 100 pounds per square inch) in the presence of a catalyst containing a metal of the iron group. However, Naragon et al. disclose that optimum results are obtained at operating pressures of about 300 to 700 pounds per square inch in the absence of a gaseous diluent and at operating pressures of about 500 to 1400 pounds per square inch in the presence of such a diluent.
U.S. Pat. No. 3,857,893, to Nozaki discloses a hydroacylation process for producing diethyl ketone from the reaction of ethylene, carbon monoxide and hydrogen at a temperature of from about 50.degree. C. to about 150.degree. C. and a pressure of about 50 psig to 2,000 psig in the presence of a catalytic amount of a cobalt carbonyl complex. Operating pressures exemplified by the Nozaki patent range from 250 psig to 500 psig.
Russian Pat. No. 813,908 discloses the use of palladium catalysts in the presence of phosphines and aqueous solutions of trifluoroacetic acid to effect the hydroacylation reaction of ethylene or propylene with carbon monoxide and hydrogen to produce diethylketone or dipropylketone. Disclosed process conditions are temperatures of 30.degree. C. to 70.degree. C. and atmospheric pressures.
The above described hydroacylation processes are generally found to be commercially non viable in that they require the use of disadvantageously high pressures and/or temperatures, produce undesirable quantities of aldehyde product, and/or proceed at undesirably slow rates and/or, in the case of processes utilizing rhodium catalysts, the catalysts have relatively short lives.